A sialic acid-containing sugar chains' biosynthesis inhibitor is excellent in suppression of inflammation or allergy. A sialic acid-containing sugar chains' biosynthesis inhibitor comprises as an active ingredient a sugar compound of the formula (1):

wherein R¹ is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a peptide residue or a sugar residue, and R² is a hydrogen atom, a sulfhydryl group, an acyloxy group, an acylthio group, an aryloxy group, an alkyloxy group, a sugar residue or a glycothio residue. The sialic acid-containing sugar chains' biosynthesis inhibitor may be used as a therapeutic agent for inflammation or the like caused by the sialic acid-containing sugar chains.